linux-kernel - RE: Oops at boot with linux-next kernel with IMA boot options

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Date:   Thu, 28 May 2020 17:36:55 +0000
From:   Roberto Sassu <roberto.sassu@...wei.com>
To:     Takashi Iwai <tiwai@...e.de>
CC:     "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Silviu Vlasceanu" <Silviu.Vlasceanu@...wei.com>
Subject: RE: Oops at boot with linux-next kernel with IMA boot options

> From: linux-integrity-owner@...r.kernel.org [mailto:linux-integrity-
> owner@...r.kernel.org] On Behalf Of Takashi Iwai
> On Thu, 28 May 2020 17:35:16 +0200,
> Takashi Iwai wrote:
> >
> > Hi Roberto,
> >
> > it seems that the recent changes in IMA in linux-next caused a
> > regression: namely it triggers an Oops when booting with the options
> >   ima_policy=tcb ima_template_fmt='d-ng|n-ng|d|ng'
> 
> And further experiment revealed that passing only ima_template_fmt=d
> is enough for triggering the bug.  Other formats don't matter.
> 
> (snip)
> > It's a KVM instance without any TPM stuff, just passed the options
> > above.  I could trigger the same bug on a bare metal, too.
> >
> > Then I performed bisection and it spotted the commit:
> > 6f1a1d103b48b1533a9c804e7a069e2c8e937ce7
> >   ima: Switch to ima_hash_algo for boot aggregate
> >
> > Actually reverting this commit fixed the Oops again.
> 
> So, looking at the fact above (triggered by "d") and this bisection
> result, it seems that the issue is specific to ima_eventdigest_init().
> The difference from others is that this has a check by
> ima_template_hash_algo_allowed(), and currently the check allows only
> SHA1 and MD5, while now SHA256 is assigned as default.  So I tested
> adding SHA256 there like below, and it seems working.
> 
> Hopefully I'm heading to a right direction...

Hi Takashi

boot_aggregate is the only entry for which there is no file descriptor.
The file descriptor is used to recalculate the digest if it is not SHA1
or MD5. For boot_aggregate, we should use instead
ima_calc_boot_aggregate(). I will provide a patch.

I see that the .file member of event_data in
ima_add_boot_aggregate() is not initialized. Can you please try
to set .file to NULL?

Thanks

Roberto

HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063
Managing Director: Li Peng, Li Jian, Shi Yanli

> thanks,
> 
> Takashi
> 
> --- a/security/integrity/ima/ima_template_lib.c
> +++ b/security/integrity/ima/ima_template_lib.c
> @@ -13,7 +13,8 @@
> 
>  static bool ima_template_hash_algo_allowed(u8 algo)
>  {
> -	if (algo == HASH_ALGO_SHA1 || algo == HASH_ALGO_MD5)
> +	if (algo == HASH_ALGO_SHA1 || algo == HASH_ALGO_SHA256 ||
> +	    algo == HASH_ALGO_MD5)
>  		return true;
> 
>  	return false;